ANDERSON – The worst fears of Donald Thomas and the Indianapolis Colts have become a reality.

Coach Chuck Pagano confirmed today the his starting left guard will require season-ending surgery after re-tearing his right quadriceps tendon during Wednesday afternoon's practice at Anderson University.

Thomas, Pagano said, was "doing a great job. (The injury is) the ugly side of football.''

Thomas, who signed to a four-year, $14 million contract during the 2013 offseason, missed the final 14 games of last season after tearing his right quad against the Miami Dolphins. He also tore a biceps tendon in the game, on the same series.

Pagano added he "just feels awful for Donald.''

The loss of Thomas is a major blow to a Colts offensive line that needs to improve on last season's performance. Not only was he expected to resume his starting spot, he was viewed as a viable option at center if first-year starter Khaled Holmes falters or suffers an injury.

With Thomas out of the mix, the available successors include Lance Louis, Jonotthan Harrison, Joe Reitz and Josh Walker. Hugh Thornton is the starting right guard.

A potential starting interior of Mewhort, Holmes and Thornton is rife with uncertainty. All will be first-year starters at those positions. Mewhort is a rookie and Holmes, a 2013 fourth-round pick, was on the field for just 12 offensive plays as a rookie.

Mewhort has taken a single-minded approach since he joined the team, and that won't change.

"I'm trying to be the best Colt I can be,'' he said.

Pagano conceded starting a rookie makes him nervous, but added Mewhort is "unflappable.

"Nothing seems to bother Jack.''

Thomas suffered the injury at practice Wednesday, remaining on the ground after it occurred, pounding the ground in disgust. After being helped to his feet he went behind a wall of players and angrily tossed a piece of equipment. He still was clearly agitated as he followed a trainer to the locker room.Thomas' serious injury is the latest to beset the Colts.

Running back Vick Ballard has undergone season-ending surgery to repair a torn left Achilles tendon suffered during non-contact drills July 25. Defensive lineman Fili Moala was placed on the injured reserve list June 11 with a torn anterior cruciate ligament in his right knee.

The Colts placed Thomas on injured reserve and signed OT Eric Pike. Pike was on the Colts' roster briefly in May and played college at Towson University.

Star reporter Stephen Holder contributed to this story. Call Star reporter Mike Chappell at (317) 444-6830. You can follow him on Twitter at @mchappell51.